Process for producing oxygen by the liquefaction and rectification of air



GARBO 2,513,306 PRocEss FOR PRoDucING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION oF AIR July 4, 195o ww ,im nl f G QN uw E R @I @u gr INVENTOI? aw f/ar ATTORNEY g 2,513,306 PRocEss Fox PRODUCING OXYGEN BY THE LIQUEFACTION July 4, 1950 P. w. GARBO AND RECTIFICATION 0F AIR 2 Sheets-Sheet 2 Filed Nov. l. 1947 Nb g Patented July V4, 1950 PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF Paul W. Garbo, Freeport, N. Y., assiguor to Hydrocarbon Research, Inc., New York, N. Y., a corporation of New Jersey Application November 1, 1947, Serial No. 783,552

1l Claims. (Cl. (i2-175.5)

This invention relates to the production of oxygen by the lliquefaction and rectification o! air, and more particularly to an economical method of obtaining oxygen in high purity and in high yield without the use of chemical reagents to eect the removal of carbon dioxide present in air.

All temperatures herein are in degrees F. and pressures in pounds per square inch gauge.

Oxygen is commonly produced by liquefaction of air and rectification at low temperatures; preferably rectification is conducted in two stages at diiferent pressures. The refrigeration necessary for llquefaction is supplied to the air, after it has been compressed and water-cooled to approximately room temperature, by indirect heat exchange with the eliluent products of rectification. However, an additional amount of refrigeration must be supplied to compensate for cold losses resulting from the differenct in enthalpy between the incoming air and the outgoing products yoi? rectification and for heat leaks into the system. Methods of supplying this refrigeration heretofore used involve compressing at least a mrtion of incoming air to pressures as high as 3000 pounds and expanding with or without the performance of Work to produce a temperature drop, or compressing 'all the incoming air to about 600 pounds and after the air has been partially cooled by the products of rectification expanding a portion of the air. These methods are wasteful from the standpoint of compressor energy and require a great deal of equipment in the form of extra compressors, intercoolers and expanders.

For economical operation it is essential to recover the cold content of the outgoing products of rectification. This is usually accomplished by passing these products in heat transfer relationship with the incoming air. In older systems, in order to avoid deposition of frost and solid carbon dioxide in the tubular countercurrent heat exchangers through which the air is passed in indirect heat exchange relation with the outgoing products of rectification, the air is treated in driers and caustic scrubbers to remove water and carbon dioxide prior to admittance of the air into the heat exchangers. Even with this treatment the exchangers had to be thawed out regularly to remove the frost (which term is used in a generic sense to include both snow and ice) which caused stopping up of the apparatus.

`More recently it has been suggested to use cold accumulators or regenerators (hereinafter reierred to as heat exchangers) of large cold absorbing capacity through which the warm incoming air and the cold products of rectification are alternately passed with periodically reversed operation so that streams of warm air are flowed through the same packing-filled spaces that the cold separated oxygen and nitrogen traversed during the previous step in the process, the high boiling impurities deposited in these spaces during the passage of air therethrough being removed by sublimation during the subsequent flow in a reverse direction of the products of rectification. The use of these reversing heat exchangers in a process in which the air is compressed to relatively high pressure results in more costly operation from the standpoint of horsepower requirements because upon every reversal, which may take place every three minutes, the volume of compressed air in the heat exchangers is lost and must be again' replaced. Moreover, in the operation of such reversing heat exchangers it is important not to let the temperature at the exit end of the exchangers drop to a point where a part Vof the air becomes liquid because this liquid adheres to the surface ci thev exchangers and is wasted upon reversal of liow.

Among the objects of this invention is to prvide a process for producing oxygen by the liquefaction and rectification of air, which process results in the production of an additional rectification product, such as oxygen of over 99% purity suitable for welding purposes', high purity nitrogen or fractions rich in krypton, argon or xenon, in addition to the usual oxygen of commerce of about to 95% purity, and notwithstanding the utilization of such additional rectiiication product or products to improve the efficiency of the purging of the heat exchange zone, such additional rectification product or `products may he Withdrawn in substantially uncontaminated condition, i. e., not contaminated with condensible constituents removed from the air; and in which such that the carbon dioxide deposited therein is efficiently removed to permit continuous operation.

Other objects and advantages of this invention will be apparent from the following detailed description.

In accordance with this invention, the rectilication system is operated to produce a main oxygen product stream having an oxygen content of from 90% to 95% suitable for many commercial uses and a main nitrogen rectiilcation product stream containing usually over 95% nitrogen, the rest being chiefly rare gases such as krypton, argon or xenon, and in addition a pure oxygen of say over 99% purity suitable for welding uses. purer nitrogen than the main nitrogen stream, fractions rich in krypton, argon, xenon, or two or more of these additional rectiication products which are herein referred to as additional rectication products to distinguish them from the main oxygen and nitrogen rectification product streams. In this specication, where reference is made to oxygen and nitrogen streams, the main oxygen and nitrogen rectication product ucts. The` air is thus cooled to a temperature close to its condensation point at the pressure existing in its ow path through the heat exchange zone, thereby substantially completely removing all carbon dioxide present in the air. The ilowof the nitrogen stream, and if desired, also of the oxygen stream, and that of the air, is periodically reversed sothat the air ilows through a path through which had previously ilowed the nitrogen or oxygen and the oxygen or nitrogen or both ilow through a path or paths through which had previously owed the air, these rectication products or product eiecting removal of carbon dioxide deposited in the heat exchange zone during the preceding step of the process. A non-reversing stream of additional or paths through which had previously flowed the air, thereby effecting removal of carbon dioxideand moisture, iiany, deposited in the heat exchange zoneduring the preceding step of the process. A non-reversing stream of additional recti'cation product, preferably oxygen suitable forwelding purposes. is passed through at least the cold end of the heat exchange zone where deposition of carbon dioxide takes place in indirect heat exchange relation with the'air, oxygen and nitrogen; the additional rectification product is thus warmed. A portion of this additional rectitlcation product is withdrawn as product uncontaminated by carbon dioxide or other condensibles removed from the air stream. The remainder is recirculated through the heat exchange zone. f

The stream of air leaves the heat exchange zone at a temperature below about 270 F. but above its condensation point. This stream is divided into two streams; one comprising the major portion of the air ows to the rectification system, the other comprising the remaining minor portion, say 15% to 35% by volume of the total air introduced into the process, is warmed to a temperature such that upon subsequent expansion little or' no liquid air is formed in the expander; the warming is preferably achieved rectitlcation product is passed through this heat" exchange zone in indirect heat exchange relation with the air and the reversing stream or streams oi' rectiflcation product. This additional stream of rectification product is thus warmed.

'A portion of this additional stream of rectication product is withdrawn uncontaminated by carbon dioxide or other condensibleconstituents deposited in the heat exchange zone from the air stream passing therethrough. The remainder of the thus warmed additional rectification product is recirculated through its iow path in the heat exchange zone augmented by more of the additional rectication product from the rectication system. The ilow path for the additional rectication product extends through at least the cold end of the heat exchange zone. By circulating a stream of additional rectification product through a fixed path extending through at least the colder portion of the heat exchange zone the tempera| ture conditions within this colder portion are -maintained such that eii'icient purging takes by heat exchange with the non-reversing stream of additional rectification product which is recirculated within the heat exchange zone. The non-reversing rectiilcation product stream also desirably ows in heat exchange relation with a reversing rectification product stream, preferably the nitrogen, to heat this stream to a temperature within 5 to 10 F., preferably 6 to 8 F.,

below the temperature of theexiting air stream, thereby conditioning the reversing rectification product stream so that it effects more eiicient removal of carbon dioxide deposited in the exr changer during the preceding step of the process. The minor portion of the vair stream which .is warmed is then expanded to produce the refrigeration necessary to compensate for cold losses resulting from the diierence in enthalpy between the incoming air and the outgoing products of rectiilcation and for heat leaks into the system. The expanded airis introduced into the low vpressure stage of the rectification system where its oxygen content is recovered.

In the rectification' system the air is rectiiied A to produce theusual oxygen and nitrogen streams and an additional recticaton product,

' such as high purity oxygen, e. g., welding grade vention a stream of air at about to 100 pounds and at a temperature of about to about 110 F. is passed through' a heat exchange zone in heat exchange relation with a stream of nitrogen and a stream of oxygen. The iiow of the air and the nitrogen and, if desired, also of the oxygen is periodically reversed so that the nitrogen and oxygen. high purity nitrogen, or a fraction rich in one or more of the rare gases including argon, neon, kr'ypton and xenon, which additional rectification product, as hereinabove described, is recirculated through at least the cold end of the heat exchange zone in indirect heat exchange relation with the air, oxygen and nitrogen passing therethrough, a portion of the recirculated additional rectification product being continuously withdrawn as product uncontaminated by condensibles removed from the air stream.

Thus, when operating in accordance with this invention, in addition to the usual oxygen and nitrogen rectification products an additional rectiiication product, desirably welding grade oxygen, is produced, and this product is recirculated through a ow path in the heat exchange zone through whiclrpath the air never passes so that it is not contaminated by carbon dioxide and other condensibles removed from the air, the recirculating stream of additional rectication product improving the emciency of the atrasos purging of the heat exchange zone.

In the accompanying drawings forming a part of this specification and showing, for purposes of exempliiication, preferred layouts of equipment for practicing the process of this invention,

Figure 1 illustrates diagrammatically a preferred layout of apparatus for practicing the process of this invention; the apparatus of this figure involves a heat exchanger of the recuperator type;

Figure 2` illustrates a modiiled arrangement of heat exchangers of the regenerator type which maybe used in lieu of the exchangers of the recuperator type shown in Figure 1;

Figure 3 illustrates diagrammatically another modiiied arrangement of apparatus for practicing the process of this invention, which modiilcation involves exchangers of the regenerator type; and 1 Figure 4 illustrates s till another modified arrangement of exchangers of the recuperator type.

It will be understood the drawings illustrate diagrammatically preferred apparatus for practicing the processof this invention and that the invention may be carried out in other apparatus. For example, any desired number of reversing exchangers of either the recuperator or regenerator type may be used in lieu of the reversing exchangers shown in the drawings; each of the reversing exchangers of the drawings may be replaced by two or more similar exchangers placed in series and/or parallel if desired; the divided or separate exchangersr hereinafter described may be disposed in a'single housing or may be constructed as separate and distinct units; other rectication systems may be used in lieu of those shown in Figures 1 and 3; the manner of pro viding refrigeration to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products periodic As the construction of the heat exchanger per se does not form a part of this invention and -as it may be of any well known type, it is believed further description thereof 'is unnecessary.

Exchanger section has two flow paths, I5 and I6. Flow path I5 is connected with path I3 by line and flow path I6 is connected with path I4 byline I8.

Exchanger B is of approximately one-fourth the volumetric capacity of exchanger A. Exchanger B comprises two sections- I9 and 2o. Section |9 consists of three flow paths, 2|, 22, 23, and section 20 consists ofthree flow paths, 24. 25 and 26 connected with paths 2|, 22 and 23 by lines 21, 28 and 29, respectively. The ex-I changer sections I9 and 20 are of the same construction as section I0 hereinabove described.

`Reversal of 110W through exchanger A is effected by a pair of reversing valves 30, 3|. Valvel 30 is connected with ilow paths I5 and I6 by lines 32, 33. Air line 34 has a branch 35 leading into valve 30 which provided with a nitrogen exit line 36. Valve 3| is'connected with ow paths I3 and I4 by lines 31 and 38. Valve 3| has a nitrogen line 39 leading thereinto and is provided with an air exit line 40.

Reversal of flow through the exchanger B is effected by a pair of reversing valves 4| andr 42. Valve 4| is connected with flow paths 24 and 25 by means of lines 43 and 44. Valve 9| has a branch line 45 leading thereinto from the air line 34 and is provided with an oxygen discharge line V46. Valve 42 is connected with ow paths 2| and 22 by lines 4'I and 48. This valve is provided with an oxygen supply line 49 and has leading therefrom an air line 5|).

i vided'with branches 52 and 53 leading into the of rectication withdrawn from the process and for heat leaks into .the system as disclosed in Figure l may be employed with the exchangers shown in the other figures of the drawings, or conversely the manner of supplying such refrigeration shown in Figure 3 may be used-with the exchangers of the other figures of the drawings.

I n the drawings, in which like reference characters indicate like parts, referring to Figure 1, A and B indicate a pair of heat exchangers; A is the heat exchanger in which ilow of air and nitrogen is reversed and B is the heat exchanger in which the flow of air and oxygen is reversed. Exchanger A comprises two sections I0 and II, section I9 having three ilow paths, namely, in-

ternal path I2 and concentric paths I9 and I9 disposed in heat exchange relation with each other. rllhe heat exchanger has in each of these paths suitable fins of heat conducting material such as copper or aluminum for promoting rapid and eflicient heat exchange between the gaseous media flowing therethrough. For purposes of illustration and in the interests of simplicity, each flow path in an exchanger is shown on the drawings as being formed by a single tube, the several paths being disposed concentrically. Actually, however, each path in each exchanger may comprise a multiplicity of tubes for ilow therethrough. One form of exchanger of the recuperator type shown diagrammatically in Figures 1 and 4, which may be used in practicing the process of this invention, is disclosed in application Serial No. 676,142, led June 12, 1946.

iiow paths I2 and 23, respectively. A line 54 leads from the exit end -of ow path I2; line 29 connecting the flow paths 23 and 26 communicates with line 54; a portion of the pure oxygen passing through paths I2 and 23 flows through line 59 to a pump or blower 56, the remainder passing through path 26 from which it is withdrawn as product through an exit line 55. Line 59 has therein a blower 56 for circulating the pure oxygen through the circulating system comprising heat exchangers 5l, 58 of the non-reversing type.

a portion of oxygen line 5I, branches 52, 53, flowpaths I2, 23 and line 59.

The rectication system comprises three columns 59, 69, 6I. Column 59 is operated at a pressure of from about 60 to 100 pounds, preferably at about 75 to 90 pounds; columns 59 and 9i at a pressure of from about 5 pounds to about 12 pounds, preferably at about 7 to 9 pounds. These columns customarily are provided with rectification plates of the bubble cap or other desired type. Air is supplied to the base portion of the high pressure column 59 throughair line 62 into which lead the lines and 50 and which passes through nonereversing heat exchangers 69 and 59, hereinaiter more fully described. Crude oxygen containing approximately 40% oxygen, the rest being chieily nitrogen, ows from the base of column 59 through line 65 which passes through a nonreversing heat exchanger 66, has therein an expansion valve 5I, and enters column 69 at 59. A nitrogen line 69 leads from the top of column 69 into a non-reversing heat exchanger lll. From this exchanger 'I9 a line 'II leads to a non-reversing heat exchanger 66. A line 'I2 leads from this non-reversing heat exchanger through the nonreversing heat -exchanger 64. Thence, line 66' 'discharges into exchanger 58 from which leads y nitrogen line 39.

Line 13 leads from the top of column 69. passes through a non-reversing heat exchanger 14 into a line having one branch 15 for returning liquid The base of column 68 is provided with a lin 19 passing through the non-reversing heat exchanger 14. leading into the low pressure column 68 at its base. The lines 19 and 88 and the heat exchanger 14 function as a reboiler; liquid oxygen iiows through line 19 through exchanger 14 in indirect heat exchange relation with the gaseous stream comprising chieiiy nitrogen passing through line 13 which causes vaporization of the liquid oxygen to take place, the oxygen vapor flowing into co1- umn 68 through line 88. Line 19 is provided with a branch line '8| having a valve 82 therein. Through this line a portion of the oxygen of about 90% to 95% purity iiowingthrough line 1 9 is drawn and. passed as reflux down through column 6I. v(apors, essentially oxygen, pass from `column 6| through line 83 into the base of column 68. Substantially pure oxygen of over 99% purity flows through a line 84 leading from the base of the column 6I through heat exchanger 85 from which a return line 86 leads into the base of column 6I. A branch line 81 having a valve 88 therein leads from the nitrogen line 13'through the heat exchanger 85 to the branch 15. The lines 84, 86, and the heat exchanger 85 function as a reboiler; liquid oxygen flowing through line 84 and heat exchanger 85 is vaporized by the nitrogen ilowing through the heat exchanger 85 in heat exchange relation therewith. The oxygen vapors flow throughline 86 into the column 6I and upwardly therethrough countercurrent to the descending stream of oxygen reiiux liquid admitted to column 6I through line 8|. A stream of oxygen having a purity of over 99% is Withdrawn from colunm 6| through line 5| leading from the base of this column.

Air line 62 is provided with a branch line 89 having a valve 98 therein; line 89 leads to the non-reversing heat exchanger 51. A minor portion oi the air iiowing through line 62 is caused to iiow through line 89 into and through the exchanger 51 in heat exchange relationship with the stream of pure oxygen passing through this exchanger, the air being thus warmed to a temperature such that no liquefaction thereof takes place on subsequent expansion in expander 9| connected with exchanger 51 by a line 92. A

' bypass line 93 having a valve 94 therein bypasses the exchanger 51 so that more or less of the air' iiowing through line 89, depending upon the position of valve 94, may be caused to bypass the heat exchanger 51, thereby controlling the temperature of the air entering the expander 9|. A line 95 leads from the expander 9| to the low pressure column 68. The main oxygen stream leaves column 68 by way of line 49 and passes through exchanger 63 before entering reversing valve 42.

In the operation of the equipment of Figure 1, air from the main air line 34 iiows through branch lines 35, 45 through the reversing valves 38, 4|, lines 33, 43, ow paths I6, 24, lines I-8, 21, ow paths I4, 2| of exchangers A and B, respectively, lines 38. 41 and the reversing valves 3|, 42, branch This line has a return portion 88 atrasos ilow paths. The major portion of the air leaving paths I4, 2| flows through line 62, non-reversing heat exchangers I63, 64 into the high pressure column 59 of the rectification system. 'I'he remaining minor portion flows through lines 89, 93,

that owing through line 93 bypassing heat exchanger 51 and that iiowing through'the heat exchanger 51 being warmed as it passes in indirect heat exchange relation wlth the warm pure oxygen stream ilowing through the exchanger 51. The thus warmed air stream mixes in line '92 with the air from line '93 to produce a mixture at a desired temperature such that upon expansion no liquid air is formed in expander 9|. 'I'he expanded air from expander 9| flows through line 95 and enters the low pressure column 60.

Nitrogen ilows from the rectication system through line 39 .into valve 3| passing through line 31, flow path I3, line I1, flow path I5, line 32, valve 38 through the nitrogen exit line 36.

Simultaneously oxygen ows from the rectification system through line 49 into valve 42, line 48, ow path 22, rline 28, ow path 25, line 44, valve 4| into and through the oxygen exit line 46. Substantially pure oxygen iiows through line 5I, branches 52, 53 and through the ow paths I2, 23 into line 54. A portion o f the pure oxygen passes from line 54 into and through line 29 and flow path 26, and is withdrawn as product through line 55. 'Ilhe remainder of the pure oxygen entering line 54 is recirculated by blower 56 through the exchanger 51 where the pure oxygen warmed in its iiow through paths I2 and 23 gives up a portion of its heat to the air stream iiowing through this exchanger. From the exchanger 51 the pure oxygen stream flows through exchanger 58 where residual heat is given up to the nitrogen stream passing through this exchanger. From this exchanger 58 the pure oxygen stream enters line 5| where it mixes with the pure oxygen flowing through this line from the rectication column 6I, the resulting mixed pure oxygen stream flowing through the branches 52, 53 into and through the iiow paths I2 and 23 as hereinabove described.

Upon reversal, which may take place everyf three minutes, the air flows inthe case of exchanger A through branch line 35, valve 38, line 32, iiow path I5, line I1, ow path I3, line 31, valve 3| into branch 48 communicating with air line 62. In the case of exchanger B the air flows through branch 45, valve 4|, line 44, path 25, line 28, path 22, line 48, valve 42, and branch 58 communicating 'with line 62. From line 62 the iiow of the air is the same as hereinabove described in connection with the preceding step. 4Nitrogen iiows from line 39 through valve 3|, line 38, flow path I4, line I8, flow path I6, line 33, valve 33, nitrogen exit line 36. Oxygen flows through line 49, valve 42, line 41, ilow path 2|, line 21, flow path 24, line 43, valve 4I through the oxygen exit line 46. Thetlow of the pure oxygen is the same as hereinabove described in connection with the preceding step.

The nitrogen, the ilow of which is periodically reversed through iiow paths I3 and I4 of exchanger section |8 and flow paths I5 yand -I6 ot exchanger section II, and the oxygen, the flow 9 of which is Periodically rever'sed through iiow paths 2|, 22 of exchanger section I9 and flow paths 24, 25 of exchanger section 20 remove from their respective iiow paths carbon dioxide and other condensibles deposited therein from the air stream flowing therethrough during the preceding step of the process. The pure oxygen stream flowing through paths I2, 23 is in part withdrawn as product after passing through flow path 26 and is in part recirculated through paths I2, 23. The recirculated pure oxygen stream gives up heat to the minor portion of the air stream fed to the expander 9| [and to the nitrogen fed to exchanger A. Since the portion of the pure oxygen withdrawn -as product never ows through a path through which the air passes, it is uncontaminated by condensibles removed from the lair stream. The portion of the pure oxygen recirculated through the exchanger sections and i9 establishes temperature conditions within the several streams passing therethrough such that the reversing oxygen and nitro-gen streams effect most eiiicient purging of carbon dioxide and other condensibles from the ow paths through which they pass.

The modification of Figure 2 differs from tha of Figure 1 chiey in that (1) two sets of regenerators are used instead o-f a pair of recuperators, and (2) the recirculated pure oxygen stream passes through the entire extent of the flow paths in the exchangers andnot through the colder end only as is the case in exchanger A of Figure 1.

Each of the regenerators of Figure 2 containsl material such as copper or aluminum of high heat transfer capacity o-ver which alternate streams of rectification product and air ow, the rectifica# tion product imparting its cold content to this material and the air recovering this cold when it flows over this material during the succeeding step of the process as is well known in this art. The two sets shown are C and D; C comprises the regenerators 96, 91, whereas D comprises the regenerators 98, 99. Extending through these regenerators Aare oxygen flow paths |00, |0|, |02 and |03, respectively. Each of these flow paths desirably is in the form of one or more tubes oi high heat conducting material, such as copper or auminum, in indirect heat exchange relationship with the material of high heat transfer capacity in thcregeneratc-rs 96 to 99.

Pure oxygen line 5| is provided with branches IM, |05, |05 and |01 which communicate with the pure oxygen flow paths E00, |0|, |02 and |03, respectively. These flow paths are provided with exit lines |08, |09, ||0 and ||I, respectively, communicating with a line I I2 having branch |3 for withdrawal of pure oxygen as product and a' second branch |I4 through which the remainder of the pure oxygen is recirculated by a blower corresponding with blower 56 (Figure 1) to the pure oxygen supply line 5| receiving pure oxygen from the rectification system as hereinabove described in connection with Figure 1. may pass through heat exchangers corresponding to exchangers 51 and 58 of Figure 1 so that the warm pure oxygen passing through this line ||4 gives up heat, say to a minor portion of the air to be expanded in order to supply refrigeration to the process and, if desired, also to the nitrogen stream passing to the exchanger set C.

Reversing valve 30 is connected with regenerator 90 by a line H5 and with regenerator 91 by line I6. Reversing valve 3| is connected with regenerator 96 by a line i I1 and with regenerator Line ||44 through regenerator 96 and oxygen through regenerator -98 and upon reversal the air flows through the regenerators 96, 99, while nitrogen ows through regenerator` 91 and oxygen ows through regenerator 99.

-In the operation of the modication of Figure 2, air at a pressure of 60 to 100 pounds and at a temperature of 70 to 110? F. supplied through line 34 ows through branches 35, 45 into and through the valves 30, 4|, lines ||6 and |20, regenerators 91, 99, lines I I8, |22, valves 3|, 42, lines 40 and 50 into the air line 62. The air is thus cooled to a temperature close to its condensation point at the pressure prevailing in these regenerators through which it ows. The thus cooled air ows through line 62 to-the rectication system, a minor portion, if desired, being expanded in expander 9| as hereinabove described in connection with the modification of Figure 1 to supply refrigeration to the process.

Simultaneously, nitrogen ows through line 39, valve 3|, line ||1, regenerator 96, line ||5, valve /30 and nitrogen exit line 30, giving up its cold to the heat transfer material in regenerator 96. Oxygen ows through line 49,.valve 42, line I2I, regenerator 90, giving up its cold to the heat transfer material therein, the oxygen exiting through line II9, valve 4| and oxygen exit line 46. Pure oxygen flows from line 5| through the branches |04 to |01, the oxygen flow paths |00 to |03, lines |00 to into line ||2. From this line a portion of the pure oxygen is withdrawn as product through line ||3 and the remainder recirculated through line ||4 to'the pure oxygen supply line 5|.

Upon reversal, which may take place every three minutes as indicated by the dotted line valve settings, the air flows through valves 30, 4I, lines II5, ||9, regenerators 96, 98, lines ||1, I2I, valves 3|, 42, lines 40, 50 into the air line 62 from which the air `flows to the rectification system as hereinabove described. Simultaneously, nitrogen flows through line 39, valve 3|, line ||9, regenerator 91, line IIB, valve 30, nitrogen exit line 36. Oxygen flows through line 49, valve 42, line |22, regenerator 99,`line |20, valve 4I into the oxygen exit line 46. Pure oxygen flows from line '5| through the same flow paths `as hereinabove described in connection with the preceding step of the process.

The nitrogen which alternately flows through one or the other of regenerators 96, 91 and the oxygen which alternately flows through one or the other of regenerators 98, 99 remove therefrom the carbon dioxide and other condens'ibles deposited therein from air during the preceding step of the process. The eiiciency of the purging action of the nitrogen and oxygen is materially improved by the recirculated stream of pure oxygen, which recirculated stream results in temperature conditions within the regenerators optimum for effecting removal of carbon dioxide by the nitrogen and oxygen streams flowing therethrough.

The modication of Figure 3 differs from those hereinabove described `chiefly in that (1) a different rectiflcation system is'employed, namely a system which results in the production of a recsection |26 of which is operated at a' pressure of about 60 to 100 pounds, preferably at about 75 to 90 pounds, and the upper section |21 of which is operated at a pressure of from pounds to l2V pounds, preferably at about 7 to 9 pounds. This column, as is customary, is provided with rectication plates of the bubble cap or other desired type. The lower section |26 communicates with condenser |26 and has a liquid collecting shelf |29 disposed immediately below the condenser for collecting liquid nitrogen. Pipe line |30 leads from shelf |29 to a non-reversing heat exchanger 3| which communicates through a pressure reducing valve |32 with the top portion of low pressure section |21. Condenser |28 acts as a reboiler for the upper section 21. l

-From the base of the lower section |26 a pipe line |33 for the flow of crude oxygen leads into a Ibranch |34 which passes` to a non-reversing heat exchange!` |35 which communicates through pipe line |36 having a pressure reducing valve |31 therein with the low pressure section |21 at an intermediate'point |38. The .other branch |39 l has an expansion valve |44 therein and communicates with a condensing coil |4| disposed in the Vtop portion of auxiliary column |42. Coil |4| communicates with the low pressure stage |21 at |43. Column |42 has a line |44 provided with a valve |45 through which a vapor side stream having a maximum concentration of argon ilows from stage |21 into column |42. In column |42 this side stream is separated into an argon vapor product which passes oil' through line |46 and an argon-oxygen-liquid fraction which is returned through line |41 to the low pressure stage 21.

A line |48 having a pressure reducing valve |49 therein leads from condenser |28 to a nitrogen line |50. A line |5| leads'from the top of the low pressure section |21, passes through ,heat exchangers |3| vand |35 and enters line |50; the

nitrogen stream flowing through line |48 enters line |50j-where it joins the stream from line |5|. Nitrogen line |50 enters a non-reversing heat exchanger |52 which has a nitrogen exit line |53 passing through a non-reversing heat exchanger |54 and communicating with line 39 entering .valve 3|. 1

. transfer material within this regenerator, the- The oxygenline 49 leads from the low pressure section |21'through a non-reversing heat exchanger |55 to l reversing valve 42. Line ||4 passes through a refrigerationsystem |56 which 'may be of any well known construction for supplying a refrigerating medium such as ethylene or methane to cool the recirculatng argon stream flowing therethrough. This refrigeration system operates to cause the ow of the refrigerating medium in indirect heat exchange relation with the argon, the rate of flowand the temperature of the various media being so controlled that enough cold is introduced by refrigeration at this point in the process to compensate for cold losses resulting from the difference in enthalpy between the. incoming air-'and the outgoing products of rectiication and for heat leaks into the system.

respectively. These regenerators may be of the same construction as those of Figure 2, differing chieily'in that argon instead of pure oxygen flows through the ilow paths |00 to |03 within the regenerators. Hence like partsof the regenerators and associated piping of Figures 2 and 3 are indicated by the same reference characters.

In the operation ofthe modiiication of Figure 3 air iiows through bran-ches 35 45, valves 30, 4|; lines ||6, |20 into the regenerators 91, 99, exiting through lines H8, |22, valves 3|, 42, lines 40, 50 and flowing into the air line 62. From this line the air passes through exchanger |55 in heat exchange relation with the oxygen stream flowing through line 49 and passing through this exchanger and then ilows through line 62' through the heat exchanger |52, where the air passes in heat exchange relation with nitrogen, into the high 'pressure section |26 of column |25. The air stream in its ilow through the regenerators 91. 99 is cooled to a temperature near its condensation point and substantially all carbon dioxide and moisture, if any, removed therefrom.

Nitrogen ilows from the rectication column |25 through line |50, passing through heat exchanger |52, line |53, heat exchanger |54, -through line 39 which enters valve 3|. From this valve nitrogen passes through line ||1, regenerator 96, and gives up its cold content to the heat nitrogen leaving the regenerator through line 5, ilowing through valve 30 and exiting through line 36. Simultaneously, oxygen iiows from the rectification column |25 through line 49, heat exchanger |55, entering valve 42 and ilowing through line |2|, regenerator 98, line ||8 and valve 4| and exiting through the oxygen exit line 46. Also at the same time a stream rich in argon ilows through line |46, enters the branches |04 to |01, ilows through the flow paths |00 to |03.

Y respectively, and exits through the branches |08 to I, respectively, into line ||2. From this line a portion of the argon-rich stream is withdrawn through ||3 as product. 'I'he remainder is recirculated by pump 56 through the refrigeration system |56, line |51, exchanger |54 where it passes in heat exchange relation with the nitrogen, and line |58 into the argon line |46 from which the argon is recirculated through the argon ow paths in regenerators 96 to 99.

Upon reversal, which may take place every three minutes,'the air ows through the regenerators 96, 98, the nitrogen through regenerator 91 and the oxygen through regenerator 99. 'I'he argon flows through the same ilow paths within the regenerators. The nitrogen, ilow of which is periodically reversed in regenerators 96, 91, and the oxygen, ow of which is periodically reversed in regenerators 99, 99, remove from their respective ilows paths the carbon dioxide and other condensibles deposited therein from the air atias'o 13 of JFigurefI, chieily in that (l) an exchanger of the recuperator type in which the flows of nitrogen and air only are reversed is used instead of 'the pair of parallel exchangers of Figure l, and (2) argon, rather than welding grade oxygen, is recirculated through the exchanger. I n Figure 4, |60 indicates an exchanger constituted of sections |6| and |62, which sections 'except as hereinafter noted may be of the same general construction as the sections of the exchangers of Figure 1 hereinabove described. Section |6| comprises four flow paths |63, |64, |66and |66; |63 is'the flow path of the recirculated stream of argon, |64 the ow path for the non-reversing stream of oxygen and |65 and |66 are the now paths through which flow of air and nitrogen are periodically reversed. Exchanger section |62 is provided with ow paths |61, |66, |69 and |10; a line |1| connects ow paths |63 and |61, a line |12 connects flow paths |64 and |66, a line 1 3 connects ilow paths |66 and |69 and a line |14 connects flow paths |66 and |10 Communicating with line |1| is a line |15 through which a portion of the argon flowing through line |1| is withdrawn and recirculated through the flow path |63 in exchanger section |6|. This recirculating system, as in the modification of Figure 1,'comprises pump 56, exchanger 51 in which the argon passes in heat exchange relation with a minor portion of the air stream owing through line 39 to expander 9|, an exchanger` 58 in which the argon stream ows in heat exchange relation with nitrogen passing through line 66 and a line |16 extending from exchanger 58 to the argon line |46 (Figure 3) which leads into the f low path |63.

Reversal of ow of the nitrogen and air streams is accomplished by reversing valves and connected piping the same as described in connection with Figure 1. Hence these valves and associated piping have been given the same reference characters as the corresponding parts of Figure 1.

In the operation of the modication of Figure 4, air is supplied through line 34 to valve 30 and, as indicated by the full line valve settings, flows through line 32, flow path |10, line |14, flow path |66, line 33 into valve 3| from which the air enters line 62. From this line a minor portion of the air flows through line 89 to exchange-r 51 where the air is warmed, the warmed air passing to expander 9| and the vexpanded air passing through line 95 into the low pressure stage of the rectification system. The remainder of the air passes through heat exchanger 63 where it is further cooled by flowing in heat exchange relation with the oxygen stream passing through line t3. The thus cooled air passes through line 62 into the high pressure stage of the rectication system. In its now through path the air is cooled to a temperature sufiicient to remove all moisture, if any, present in the a'r. In its ow through path |66 the air is cooled to a temperature near its condensation point and all carbon dioxide is removed therefrom and deposited in ilow path |66.

Nitrogen flows through line 65', exchanger 58, line 36, valve 3|, line 31, flow path |65, line |13, iiow path |69, line 33, valve 30 to the nitrogen exit line 36. Simultaneously oxygen flows through line 49,.exchanger 63, ow path |64, line i12, flow path |66 to the oxygen exit line |16 leading from the exit end of the ow path |66. Argon flows from line |46 through flow path |63 into line |1|. A portion of the argon flowing through line |1| is recirculated through line |15 by pump 56, flowing as hereinabove described through exchangers 51 and 66, line |16 into line |46 where it mixeswith the argon from the rectiflcation system, the resultant stream passing through flow path |63. The remainder of the argon from line |1| nows through now path |61 and is withdrawn through the argon line |11.

Upon reversal, as indicated by the dotted setting of reversing valves 30 and 3| which reversal may take place every three minutes, air flows throughvalve 30, line 33, ow path |69, line |13, ow path |65, line 31, valve 3| into line 62. From this line the now of the airis the same as described above in connection with the preceding step. Nitrogen flows from line 65 through ex-` changer 58,l line 39, Valve 3|, line 38, now path |66, line |14, flow path |10, line 32, valve 30 to the nitrogen exit line 36. The nitrogen on each reversal yflows through the path through which had previously passed the air and removes from this path carbon dioxide and other condensibles removed from the air stream during the preceding step of the process. The oxygen and argon streams flow through their respective now-paths the same as during the preceding step of the process, i. e., no reversal of flow of either of these streams takes place. Since the argon stream employed to condition the nitrogen stream to effect more eflicient purging ows through a path in exchanger |60 through which the air never passes, it is not contaminated by condensibles removed from the air stream.

Instead of argon, streams rich in krypton, xenon, neon or relatively pure nitrogen, produced for example in an auxiliary column associated with the rectification system by rectication of a side stream containing the desired constituent or constituents, may be recirculated through the ow paths |63 in Figure 4 and |00 to |03 of Figure 2, a portion of the recirculating stream being withdrawn as product and the remainder retained in the circulating system. In the modifications of Figures 2 and 3, instead of passing the recirculated additional rectification product through the entire extent of the regenerators, the flow paths through the regenerators may be provided with a take-off line at a point intermediate the ends of the ow paths for withdrawing a portion of the additional rectication product to be recirculated corresponding to the arrangement shown in Figures 1 and 4. Desirably, this point of withdrawal is positioned in the flow path where the temperature is within the range of 120 F. to 175 F. `Also the additional rectification product which is recirculated may be caused to pass through the entire extent of the flow paths in the exchangers of Figures 1 and 4 instead of through the colder portion only of certain of these exchangers as shown in Figures 1 and 4.

One example of the operation of the process of this invention in the apparatus shown in Figure l is described below. It will be understood this example is given for purposes of exemplication only and the invention is not limited thereto. The example refers to an oxygen plant operating in a locality where the atmospheric pressure is 14.6 pounds per square inch absolute.

Air under pressure of about pounds and a temperature of 70 F. is supplied through line 34, llows through branches 35, 45, valves 3|), 4|, passing through lines 33, 43, ow paths I6, 24, lines i6, 21, ow paths lll, 2|, lines 36, 41, valves 3|, 42, linesr40, 56, respectively, into line 62. The air enters line 62 at a temperature of 272 F.

- l About 28% by volume of the air at this temperature is passed through line89, ows through exchanger 51 where it passes in heat exchange relation with a recirculating stream of pure oxygen which enters the exchanger at a temperature of 217.5 F.; the temperature of the air is thus increased to 242 F. and the temperature of the oxygen reduced to 256 F. The thus warmed air enters expander 9| where it is expanded to a pressure of approximately 10 pounds and a temperature of 302.2 F., at which temperature and pressure it enters the low pressure column 60 through line 95.

The remaining 72% of the air ows through heat exchanger 63 where its temperature is reduced to 273.8 F. by heat exchange with the oxygen flowing through this exchanger; the oxygen inlet temperature to this exchanger is 288.2 F.; it leaves the exchanger at a temperature of 280 F. The air then iiows through exchanger 64 where its temperature is reduced to' 274 F. by heat exchange with the nitrogen owin-g through this exchanger. The nitrogen enters at a temperature of 292 F. and leaves at. 290 F. From exchanger 64 the air at a temperature of 274 F. enters the bottom of high pressure column 59. v

High pressure column 59 is operated ata presatrasos a temperature of 288.2 F. passes through line 8| into the pure oxygen stripping column. 6I which is operated at a pressure of approximately 10.5,pounds. From the base of column 6| substantially pure oxygen at a temperature of 287 F. ilows throughline 84, heat exchanger 85. where it passes in heat exchange relation with the nitro'gen stream owing through exchanger 85, returning to column 6| through line 86 where the oxygen vapors pass countercurrent to the descending stream of reux liquid oxygen introduced through line 8| as hereinabove described. From the top of column 6| oxygen vapors ow into the base of column 60 through line 83. Substantially pure oxygen (over 99% purity) is withdrawn through line .5| at a temperature of 287 F. This oxygen mixes with the circulating stream of oxygen which leaves exchanger 58 at a temperature of 287 F. and at this temperature enters line 5I; the resultant oxygen stream ilows through branch lines 52, 53 through the sure of about 88 pounds. Crude oxygen at a temperature of 275.3 F. is withdrawn through line 65 and passed through the heat exchanger 66 where its temperature is reduced to 277.6 F., at which temperature it ows through expansion valve 61 where it is flashed to a pressure 'of about 9 pounds and a temperature ofabout 307 F., at which pressure and temperature it enters the low pressure column 60. The nitrogen stream passing through exchanger 66 enters at a temperature of 294.8 F. and leaves at a tem.- perature of 292 F. Nitrogen at a temperature of. 282.4 F. leaves the top of high pressure column 59, part of this nitrogen being recirculated through ,heat exchanger 85 to supply heat to the oxygen stream passing therethrough. From exchanger 85 the nitrogen flows to branch 115. The remainder of the nitrogen passes through exchanger 14 in heat exchange relation with the oxygen stream passing through this exchanger. v

The nitrogen stream leaving exchanger 14 is divided so that part flows through branch 15 and this part, along with nitrogen owing into line 15 from exchanger 85, is returned as reflux to column 59. The other part at a temperature of about 282 F. enters exchanger 10 and leaves at a temperature of 309.4 F. The nitrogen is `then expanded through valve 18 to a pressure of about 8 pounds and a temperature of 312.3 F., at which pressure and temperature it enters 'low pressure column 60 at 11.

Nitrogen rectication product at a temperature of 312.3 F. leaves low pressure column 60 through line 69 and passes through exchanger 10, its temperature thereby being increased to 294.8 F. It then passes through exchanger 66, its temperature thereby being increased to 292 F., thereafter through exchanger 64, its temperature being thereby increased to 290 F., and

through exchanger 58, its temperature being thereby increased to about 280 F. At this temperature it flows through reversing valve 3|, line 31, ow path I3, line I1, 110W path |5,. line 32, valve 30 and nitrogen exit line 36, leaving this line at a temperature of 60 F. and a pressure of about 0.1 pound.

Oxygen ofv approximately 95% purity and at flow paths I2, 23. The oxygen leaves these now paths at a temperature of about 219 F; Approximately 6% of the oxygen flowing into line 54`continues its flow through ow path 26 and leaves the ow path through line 55 at a temperature of 50 F. and a pressure of about 1 pound. The remainder of the oxygen owing into line 54 is recirculated by pump 56 through the exchangers 51, 58 into the return line 5|; the oxygen enters 4exchanger 51 at a temperature of 217.5 F. and leaves at 256 F.; it enters ex changer 58 at 256 F. and leaves at 287 F.

Oxygen of approximately concentration ilows from column 60 through line 49 at a temperature of 288.2 F. and a pressure of about 10 pounds, passes through heat exchanger 6I where its temperature is increased to about 280 F., at which temperature is enters reversing valve 42, flows through line 48, ow path 22, line 28, iiow path 25, leaving this ow path at a temperature of about 50 F. and a pressure of about 1 pound.

Upon reversal. which may take place every three minutes, the air ows through paths II, I3 in exchanger A and 25, 22 in exchanger B: nitrogen iiows through paths I4, I6 of exchanger g A and oxygen through paths 2|, 24 of exchanger B. The iow of the various streams is otherwise substantially the same as hereinabove described and the temperature and pressure conditions remain the same. The nitrogen and oxygen streams of about 95% concentration in their flow remove by sublimation and evaporation carbon dioxide and moisture, if any, deposited by the air during the preceding step. Thus upon each reversal the reversing nitrogen and oxygen rectilcation product streams effect removal of the carbon dioxide and frost, if any, deposited in the paths through which the air had passed during the preceding step of the process.

In the operation of the process of this invention it is preferred to eiect removal of moisture and carbon dioxide both in accordance with the process of this invention. It will be understood. however, that, if desired, the moisture may be removed from the air by any conventional means and dry air containing carbon dioxidel passed through the exchanger or exchangers as hereinabove disclosed. In the event that dry air is supplied to the process and the exchanger system is similar to that of Figure 1, reversing -valves 30, 4| may advantageously be moved to the position between exchanger sections I0 and II of exchanger 'A and I9 and 20 of exchanger B so to 12 pounds.

atraso@ that reversal of the air and nitrogen streams occurs only in exchanger section I and ofthe air and oxygen streams occurs only in exchanger section I9 wherein the carbon dioxide is deposited by the air stream. The reversing valve 30 of Figure 4 may be similarly positioned when the equipment ofy these iigures is operated with dry air. Operation of such an arrangement is carried out so that the temperature at the warm end of exchanger sections I0 and i9 of Figure y1 and |61 of Figure 4 is at least slightly higher than the temperature at which the carbon dioxide begins to deposit from the air stream. In general; the air entering the warm end of these exchangers should be at a temperature in the range of about 110 to 160 F., the exiting product streams being about 10 to 15 F. colder.

As a desirable operating range the air is admitted to the inlet of the exchangers at a temperature of from 70 to 110 F. and a pressure of 60 to 100 pounds, preferably '75 to 90 pounds. The air in its iiow through exchanger sections I I and of Figure 1 and |62 of Figure 4 is cooled to a temperature of 110 F. to 160 F. and at t tiiication product enters the exchangers at a temperature of from 288 to 293 F., the nitrogen enters at a temperature 0f from 265 to 285 F., and both the oxygen and nitrogen leave the exchangers at a temperature of from 60 to 100 F. In the modifications involving split or sectional exchangers, e. g., the modifications of Figures 1 to 4, the oxygen leaves exchanger sections l9 and IBI of Figures 1 and 4, respectively, and the nitrogen leaves exchanger sections I0 and ISI of Figures 1 and 4, respectively, at a temperature of from about 120 to 175 F. The high pressure stage of the rectiiication system is maintained at about 6 0 to 100 pounds and the low pressure stage at about 5 small pressure drop in flowing through the exchangers.

In those modifications involving division of the' air stream into two streams with a minor portion of the airv passed to the expander to supply refrigeration to the process from 15% to 35% of the total air introduced into the process may thus be expanded. y

Operating in accordance with this invention it is found that substantially complete removal of carbon dioxide takes place from the air stream prior to its introduction into the rectification system, permitting eflicient rectification of the air to produce oxygen of about 95% purity suitable for most commercial uses and also pure oxygen or other desired rectification product. The air flow paths upon each reversal are purged to remove therefrom the carbon dioxide and frost, if any, thereby permitting continuous operation. This purging is accomplished more efliciently and at the same time pure oxygen or other rectication product stream instrumental in improving the eiiiciency of the purgingis withdrawn as product uncontaminated by condensibles removed from the air.

The expressions reversing the flow of air and nitrogen or of air and oxygen and reversal The several streams suffer only a comprehensive sense to include the iiow ar-` rangement of Figures 2 and 3 'in which the nonreversing recirculating rectification product stream ows through a path consisting of four sections in parallel as well as paths consisting of sections in series'as shown, for example, in Figure 1.

Since certain changes may be made in carry-- ing out the above processes without departing from the-scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative'and not in a limiting sense. This application is directed to species of the generic invention disclosed and claimed in my co-pending application Serial No. 783,551, filed November 1, 1947.

What is claimed is:

1. A process for producing oxygen .by the liquefaction and rectification of air, which cornprises passing streams of nitrogen and oxygen rectification products through nitrogen and oxygen iiow paths respectively in a heat exchange zone, passing a stream of air through another path in said heat exchange zone to recover the cold content of the nitrogen and oxygen rectication products. cooling the air to a temperaturelclose to its condensation point at the pressure prevailing in its vflow path through said heat exchange zone and effecting substantially complete removal of carbon dioxide from the air, in its passage through said heat exchange zone, subjecting the thus cooled air to rectification to produce said oxygen and nitrogen rectiiication products and also an additional rectification product,. periodically reversing the flow of air and nitrogen through their respective paths in said heat exchange zone, whereby upon each of said reversals the nitrogen substantially completely removes the carbon dioxide deposited during the preceding step of the process in the path through which the nitrogen-flows, passing the stream of said additional rectication product through a path extending through at dleast the colder portion of said heat exchange zone in indirect heat exchange relation with the air and the nitrogen steams passing4 through their respective paths in said heat exchange z'one, removing a portion of said additional rectification product as product uncontaminated by condensibles removed from the air stream and recirculating the remainder through its flow path extending through at least the colder portion of said heat exchange zone. A

2. A process for producing oxygen by the liquefaction and rectiiication of air, which comprises passing streams of nitrogen and oxygen rectification products through nitrogen and oxygen flow paths respectively in a heat exchange zone, passing a stream of air through another path in said heat exchange zone to recover the cold content of the nitrogen and oxygen rectification products, cooling the air to a temperature close to its condensation point at the pressure prevailing in its flow path through said heat exchange zone and effecting substantially complete' removal of carbon dioxide from the air in its `pure oxygen, periodically reversingthe ilow of air and nitrogen through their respective paths in said heat exchange zone, whereby upon each of saidreversals the nitrogen substantially completely removes the carbon dioxide deposited during the preceding step oi' the process in the path through which the nitrogen flows, passing a.

stream o! said substantiallyfpure oxygen through a path extending through at least the colder portion of saidheat exchange zone in indirect heat exchange relation w`ith the air and the nitrogen stream passing through their respective paths in said heat exchange zone, removing a portion of said substantially pure oxygen as product uncontaminated by condensibles removed from the air stream and recirculating the remainder of said substantially pure oxygen through its flow path 'extending through at least the. colder portion of said heat exchange zone.

3. A process for producing oxygen by the liquefaction and rectication of air, which comprises passing va stream of nitrogen rectification product through a path in a heat exchange zone, passing a stream of air through another path in said heat exchange zone, passing a stream of oxygen rectiiication product through a path in a second heat exchange zone, passing a second stream of air through another path in said second heat exchange zone, cooling the air during its passage through said iirst and second heat` exchange zones to a temperature close to its condensation point at the pressure prevailing in the air flow paths through said heat exchange zones and effecting substantially complete removal oi. carbon dioxide from the air in its passage through said heat exchange zones, subjecting the thus cooled al1` to rectification to produce said omgen and nitrogen rectification product streams and also an additional rectiiication product, periodically reversing the flow of air and nitrogen and of the air and oxygen through their respective paths in said heat exchange zones, whereby upon each of said reversals the nitrogen and oxygen substantially completelyremove lthe carbon dioxide deposited during the preceding step of the process in the paths through which the nitrogen and" oxygenflows respectively, passing streams of said additional rectiiication product through -a path extending through at least the colder portion of both of said heat exchange zones in indirect heat exchange relation with (1) the air and nitrogen in said rst heat exchange zone, and (2) the air and oxygen insaid second heat exchange zone,

removing a portion of said additional rectiiicaa tion product as product uncontaminated by conother path in said heat exchange zone to recover the cold content of the nitrogen and oxygen rectication products. cooling theair to a 4tem-- perature close to its condensation point at the pressure prevailing in its ilow path through said heat exchange zone'and effecting substantially complete removal of carbon dioxide fronr the air in its passage through said heat exAc/hange zone,

dividing the air stream into major` and,minor l portions, passing the major portonio thehigh pressure stage of the rectiiication system, passing an additional stream of rectiilcatioiiI product through a ilow path extending through at least the colder portion of said heat exchange zone in heat exchange relation with isaid' streams of nitrogen and oxygen rectiiication products vthere-v by warming said additional stilam ofrectitlcation product, dividing said warmed stream into two streams, withdrawing one of Vsaid streams as product, recirculating the otherj,of said streams through its iiow path in said heat exchange zone, the said recirculated stream flowing in indirect heat exchange relation with (1) said minor portionof the air stream thereby warming said minor portion to a temperature such that said minor portion can thereafter"l be expanded without substantial liquefaction. and (2) at least a portion of the said nitrogen stream prior to its entry into said heat exchange zone thereby warming said nitrogen stream'to a temperature within 5 to 10 F. of the temperature of the air stream leaving said heat exchange zone, expanding said warmed minor portion of the air to produce refrigeration in amount suiiicient to compensate for cold losses resulting from the difierence in enthalpy between the incoming air and the outgoing products of rectication and for heat leaks into the process, introducing the expanded air into the low pressure stage of the rectication system, rectifying said major and minor portions of air to produce said streams of oxygen, nitrogen and additional rectification products, and periodically reversing the iiow of air and nitrogen through their respective paths in said heat exchange zone, whereby upon each of said reversals the nitrogen substantially completely removes the carbon dioxide deposited during the preceding step of the process in the path through which the nitrogen ows.

5. A process for producing oxygen by the liquefaction and rectification of air in a rectification system involving high and 10W pressure stages, which comprises passing streams of nitrogen and oxygen rectiiication products through nitrogen and oxygen iiow paths respectively in a heat exchange zone, passing a stream of air through another path in said heat exchange zone to recover the cold content of the nitrogen and oxygen rectification products, cooling the air to a temperature close to its condensation point at the pressure prevailing in its flow path through said heat exchange zone, dividing the air stream into major and minor portions, passing the major portion to the high pressure stage of the rectication system, passing a stream of substantially pure oxygen. through a ow path extending .through at least the colder portion of said heat exchange zone in heat exchange' relation with said streams of nitrogen and oxygen rectiiication products thereby warming said stream of pure oxygen, dividing said warm stream of pure oxygen into two streams, withdrawing one of said streams as product, recirculating the other ot said streams through its ow path in said heat exchange zone, the said recirculated stream ilrst iiowing in indirect heat exchange relation with (1) said minor portion of the air stream thereby warming said minor portion to a temperature such that said minor portion can thereafter bg y 2l expanded without substantial liquetaction, and (2) at least a portion of the said nitrogen stream prior to its entry into said heat exchange zone thereby warming said nitrogen stream to a temperature within 5 to 10 F. of the temperature of the air stream leaving said heat exchange zone.

expanding said warmed minor portion of the air to produce refrigeration in amount sufficient to compensate for cold losses resulting from the difference in enthalpy between the incoming ir and the outgoing products of rectification and for heat leaks into the process, introducing the expanded air into the low pressure stage 'of the rectification system, rectifying said major and minor portions of the air to produce said oxygen, nitrogen and pure oxygen streams, and periodically reversing the flow of air and nitrogen through their respective paths in said heat exchange zone, whereby upon each of said reversals the nitrogen substantially completely removes the carbon dioxide deposited during the preceding step of the process in the path through which the nitrogen ows.

6. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of nitrogen rectification product through a path in a heat exchange zone, passing a stream of ai;` through another path in said heat exchange zone, passing a stream of oxygen rectification product through a path in a second heat exchange zone, passing a second stream of air through another path in said second heat exchange zone, cooling the air during its passage through said first and second heat exchange zones to a temperature close to its condensation point at the pressure prevailing in said flow paths through said heat exchange zones and effecting substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zones, subjecting the thus cooled air to rectification to produce said oxygen and nitrogen rectification product streams and also an additional stream consisting ofsubstantially pure oxygen, periodically reversing the flow of air and nitrogen and of the air and oxygen through their respective paths in said heat exchange zones, whereby upon each of said reversals the nitrogen and oxygen substantially completely remove the carbon dioxide deposited during the preceding step of thel process in the paths through which the nitrogen and oxygen flows respectively, passing a stream of said substantially pure oxygen through a path extending through at least the colder portions of both of said heat exchange zones in indirect heat exchange relation with (1)- the air and nitrogen in said first heat exchange zone and (2) the air and oxygen in said second heat exchange zone, removing a portion of said substantially pure oxygen as product uncontaminated by condensibles removed from the air stream and recirculating the remainder through its flow paths extending through at least the colder portions of said heat exchange zones.

7. A process for producing oxygen by the liquefaction and rectification of air in a rectification system involving high and low pressure stages, which comprises passing a stream of nitrogen rectification product through a path in a heat exchange zone, passing a stream of air through another path in said heat exchange zone, passing a stream of oxygen rectication lproduct through a path in a second heat exchange zone, vpassing a second' stream of air through another path in said second heat exchange zone, cooling the air during its passage through said first and second heat exchange zones to a temperature close to its condensation point at the pressure prevailing 'in said flow paths through said heat exchange zones and effecting substantially complete removal of carbon dioxide from the air in its passage through said heat exchange zones, dividing the thus cooled air leaving said first andsecond heat'exchange zones into major and minor portions, passing the major portion to the high pressure stage of the rectification system, passing a stream of substantially pure oxygen through a flow path extending through at least the colder portions of said heat exchange zones in indirect heat exchange relation'with the air and nitrogen and the air and oxygen passing therethrough, thereby warming said stream of substantially pure oxygen dividing said warm stream of substantiallyf" pure oxygen into two streams, withdrawing one of said lstreams as product, recirculating the other of said streams through its flow path in said heat exchange zones, the recirculating stream flowing in indirect heat exchange relation with (1) said minor portion of the air stream thereby warming said minor portion to a temperature such that said minor portion can thereafter be expanded without substantial liquefaction and (2) at least a portion of the said nitrogen stream prior to its entry into the first mentioned heat exchange zone thereby warming said nitrogen stream to a temperature within 5 to 10 F. of the temperature of the air stream leaving said first mentioned heat exchange zone, expanding the said warmed minor portion of the air to produce refrigeration in amount sufficient to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the process, introducing the expanded air into the low pressure stage of the rectification system, rectifying said major and minor portions of the air to produce said oxygen, nitrogen and substantially pure oxygen, and periodically reversing the flow of air and nitrogen and of the air and oxygen through their respective paths in said heat exchange zones, whereby upon each of said reversals the nitrogen and oxygen substantially completely remove the carbon dioxide deposited during the preceding step of the process in the paths through which the nitrogen and oxygen flows respectively.

8. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of nitrogen rectification product through one of a pair of regenerators while simultaneously passing a stream of air through the other of said regenerators, passing a stream of oxygen rectification product through one of a second pair of regenerators while simultaneously passing air through the other of said pair of regenerators, cooling the air passing through said regenerators to a temperature close to its condensation point at the pressure prevailing in its flow path through said regenerators, subjecting the thus cooled air to rectification to produce said oxygen and nitrogen rectification products and an additional rectification product, passing a stream of additional rectification product through at least the colder portions of all of said regenerators in indirect heat exchange relation with the gaseous media passing therethrough, removing a portion ofv said additional rectification product as product uncontaminated by condensibles removed from the air stream, recirculatng the remainder through its ow path extending through at least the colder portions of said regenerators and periodically reversing the ilow of nitrogen and air through the respective regenerators of the rst-mentioned pair and the now of oxygen and air through the respective regenerators of the second-mentioned pair,

y thereby eecting the substantially complete reuct through one of a pair of regenerators while simultaneously passing a stream of air through the other of said regenerators, passing a stream of oxygen rectication product through one of a second pair of regenerators while simultaneously passing air through the other of said pair of regenerators, cooling the air passing through said regenerators to a temperature close to its condensation point at the pressure prevailing in its ilow path through said regenerators, subjecting the thus cooled air to rectification to producesaid oxygen and nitrogen rectiiication product, passing the stream of substantially pure oxygen rectiiication product through at least the colder portions of all of said regenerators in indirect heat exchange relation with the gaseous media passing therethrough, removing a portion ,of said substantially pure oxygen rectification product as product uncontaminated by condensibles removed from the air stream and recirculating the remainder through its ow path extending through at least the colder portions of said regenerators, and periodically reversing the flow of nitrogen and air through the respective regenerators of the first-mentioned pair and the flow of oxygen and air through the respective regenerators of the second-mentioned pair, thereby effecting the substantially complete removal of carbon dioxide from the air in its passage through said regenerators and upon each reversal eiecting the substantially complete removal of the carbon dioxide thus deposited in the regenerators during the preceding step of the process.

10. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of nitrogen rectiiication product through one of a pair of. regenerators while simultaneously passing a stream of air `through the other of said regenerators, passing a stream of oxygen rectification product through one of a secondpair of regenerators while simul-r taneously passing air through the other of said pair of regenerators, cooling the air passing through said regenerators to a temperature close to its condensation point at the pressure prevailing -in its iiow path through said regenerators, subiecting the thus cooled lair to rectiiication to produce said oxygen and nitrogen rectification products and argon, passing a stream of argon through said regenerators in indirect heat exchange relation with the gaseous media passing therethrough, withdrawing a portion of the argon as product, passing the remainder in heat exchange relation with a refrigerant and also in heat exchange relation withat least a portion of the stream of nitrogen supplied to the ilrstmentioned pair of regenerators. thereby cooling said argon, recirculating the cooled argon through its iiow path in said regenerators and periodically reversing the iiow of nitrogen and air through the respective regenerators of the firstmentioned pair and the ow of oxygen and air through the respective regenerators of the second-mentioned pair, thereby effecting the substantially complete removal of the carbon dioxide thus deposited in the regenerators during the preceding step of the process.

11. A process for producing oxygen by the liquefaction and rectiiication of air, which comprises passing nitrogen and oxygen rectification products through a heat exchange zone, passing a stream of air through said heat exchange zone to recover the cold content of the nitrogen and oxygen rectification products thereby cooling the air to a temperature close to its condensation point at the pressure prevailing in said heat exchange vzone and effecting substantially complete rer'noval of carbon dioxide from the air in its passage through said heat exchange zone, subjecting the thus cooled air to rectiflcation to produce said oxygen and nitrogen rectification products and also an additional rectication product, periodically reversing the flow of air and nitrogen through said heat exchange zone, ypassing the said additional rectification product through at least the colder portion oi said heat exchange Azone in indirect heat exchange relation with the air and the nitrogen passing through said heat exchange zone, and removing a, portion of said additionallrectication product. as product uncontaminated by condensibles removed from the air stream and recirculating the remainder through at least the colder portion of said heat exchange zone.

VPAUL. W. GARBO.

No references cited. 

1. A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES PASSING STREAMS OF NITROGEN AND OXYGEN RECTIFICATION PRODUCTS THROUGH NITROGEN AND OXYGEN FLOW PATHS RESPECTIVELY IN A HEAT EXCHANGE ZONE, PASSING A STREAM OF AIR THROUGH ANOTHER PATH IN SAID HEAT EXCHANGE ZONE TO RECOVER THE COLD CONTENT OF THE NITROGEN AND OXYGEN RECTIFICATION PRODUCTS, COOLING THE AIR TO A TEMPERATURE CLOSE TO ITS CONDENSATION POINT AT THE PRESSURE PREVAILING IN ITS FLOW PATH THROUGH SAID HEAT EXCHANGE ZONE AND EFFECTING SUBSTANTIALLY COMPLETE REMOVAL OF CARBON DIOXIDE FROM THE AIR IN ITS PASSAGE THROUGH SAID HEAT EXCHANGE ZONE, SUBJECTING THE THUS COOLED AIR TO RECTIFICATION TO PRODUCE SAID OXYGEN AND NITROGEN RECTIFICATION PRODUCTS AND ALSO AN ADDITIONAL RECTIFICATION PRODUCT, PERIODICALLY REVERSING THE FLOW OF AIR AND NITROGEN THROUGH THEIR RESPECTIVE PATHS IN SAID HEAT EXCHANGE ZONE, WHEREBY UPON EACH OF SAID REVERSALS THE NITROGEN SUBSTANTIALLY COMPLETELY REMOVES THE CARBON DIOXIDE DEPOSITED DURING THE PRECEDING STEP OF THE PROCESS IN THE PATH THROUGH WHICH THE NITROGEN FLOWS, PASSING THE STREAM OF SAID ADDITIONAL RECTIFICATION PRODUCT THROUGH A PATH EXTENDING THROUGH AT LEAST THE COLDER PORTION OF SAID HEAT EXCHANGE ZONE IN INDIRECT HEAT EXCHANGE RELATION WITH THE AIR AND 